+/// Check if we can delinearize the subscripts. If the SCEVs representing the
+/// source and destination array references are recurrences on a nested loop,
+/// this function flattens the nested recurrences into seperate recurrences
+/// for each loop level.
+bool
+DependenceAnalysis::tryDelinearize(const SCEV *SrcSCEV, const SCEV *DstSCEV,
+ SmallVectorImpl<Subscript> &Pair) const {
+ const SCEVAddRecExpr *SrcAR = dyn_cast<SCEVAddRecExpr>(SrcSCEV);
+ const SCEVAddRecExpr *DstAR = dyn_cast<SCEVAddRecExpr>(DstSCEV);
+ if (!SrcAR || !DstAR || !SrcAR->isAffine() || !DstAR->isAffine())
+ return false;
+
+ SmallVector<const SCEV *, 4> SrcSubscripts, DstSubscripts, SrcSizes, DstSizes;
+ SrcAR->delinearize(*SE, SrcSubscripts, SrcSizes);
+ DstAR->delinearize(*SE, DstSubscripts, DstSizes);
+
+ int size = SrcSubscripts.size();
+ int dstSize = DstSubscripts.size();
+ if (size != dstSize || size < 2)
+ return false;
+
+#ifndef NDEBUG
+ DEBUG(errs() << "\nSrcSubscripts: ");
+ for (int i = 0; i < size; i++)
+ DEBUG(errs() << *SrcSubscripts[i]);
+ DEBUG(errs() << "\nDstSubscripts: ");
+ for (int i = 0; i < size; i++)
+ DEBUG(errs() << *DstSubscripts[i]);
+#endif
+
+ // The delinearization transforms a single-subscript MIV dependence test into
+ // a multi-subscript SIV dependence test that is easier to compute. So we
+ // resize Pair to contain as many pairs of subscripts as the delinearization
+ // has found, and then initialize the pairs following the delinearization.
+ Pair.resize(size);
+ for (int i = 0; i < size; ++i) {
+ Pair[i].Src = SrcSubscripts[i];
+ Pair[i].Dst = DstSubscripts[i];
+
+ // FIXME: we should record the bounds SrcSizes[i] and DstSizes[i] that the
+ // delinearization has found, and add these constraints to the dependence
+ // check to avoid memory accesses overflow from one dimension into another.
+ // This is related to the problem of determining the existence of data
+ // dependences in array accesses using a different number of subscripts: in
+ // C one can access an array A[100][100]; as A[0][9999], *A[9999], etc.
+ }
+
+ return true;
+}